When you've made the major revisions to your novel and you are satisfied with the way the plot flows and twists, with the climax and resolution, and when the characters and settings feel as vibrant and believable as you can make them, it's time to sweat the small stuff. You'll need to polish every scene, every paragraph, and every sentence so your manuscript will be as perfect as it has to be in order to pass muster with an agent or editor.